A magnetic disk drive is a digital data storage device that stores digital data on a magnetic medium known as a disk. The disk, in general, comprises a plurality of concentric tracks for storing the digital data. Data is stored on the tracks of the disk in the form of magnetic polarity transitions induced into a magnetic layer covering the disk. During operation of the disk drive, the disk is rotated about an axis by a spin motor at a substantially constant angular speed. To perform a transfer of data with the disk, a transducer, known as a head, is centered above a track of the rotating disk. Once centered, the head can be used to transfer data to the predetermined track (during a write operation) or to transfer data from the track (during a read operation). During a write operation, for example, a write current is delivered to the centered head to create an alternating magnetic field in a lower portion of the head that induces magnetic polarity transitions onto the track. During a read operation, the centered head senses magnetic fields emanating from the magnetic polarity transitions on the moving track to create an analog read signal representative of the data thereon.
In some disk drive systems, a head with a single element is used to perform both read and write operations. That is, the same element that induces the polarity transitions into the track during a write operation, senses the polarity transitions during a read operation. Other disk drive systems use dual element heads that include both a write element and a separate read element. Dual element heads are advantageous because they allow each element to be optimized for performing a single unique function (i.e., reading or writing). Dual element heads of the past, however, are known to produce a nonlinear servo position signal transfer function that can significantly degrade servo performance.
FIG. 1A illustrates an ideal servo position signal transfer function 10 for a dual element head having a magnetoresistive (MR) read element. Note the linearity of the ideal transfer function. FIG. 1B, on the other hand, illustrates an actual servo position transfer function 12 that can be expected in practice. As illustrated, this servo position transfer function is nonlinear in the region 14 between the track centerlines. This nonlinearity is undesirable because it can result in, for example, increased tracking error, longer seek settling times, increased data channel error rate, and decreased reliability.
Therefore, a need exists for a dual element head that avoids some of the problems associated with dual element heads of the past.